Got a problem with a Laney amp...

My Laney R4H head dicided to blow both internal fuses the other week too. I thought, "oh well there coulda been a power surge or something, that's what fuses are for."

I took the old fuses out, got some exact replacements (20mm Time delay [email protected]) but when I powered the amp up, they instantly blew. I can't see what the problem is. Has anyone got any ideas or clues please?

Here's a couple of photos of the board if they help jog anyone's memories.

Thanks,

Josh.

 

Fuses blow to PROTECT your amp, to shut the power off before internal components get fried. If the fuse blows twice, there is something terribly wrong. Get it to a QUALIFIED tech and he'll put every internal component on a meter to see where the problem lies. You can't always visually see damage, though sometimes you can.

 

Yeah, I know, it's a good point to stress too.

I only replaced them once and when they blew a second time I stopped. I hope everyone else does the same and doesn't try again at that point!

I tried replacing them to see if the fuses had blown due to a spike in the mains supply. Obviously not this time, heh.

I am trained in electronic theory and have built quite a few pieces of equipment before (radio transmitters/recievers and test equipment)


I just asked here because if it was a problem someone else had encountered and could point out which component was at fault, I could narrow down my testing.

If not, I'll just have to test the circuit from beginning to end.

 

I can't really tell anything from those pictures, but TYPICALLY blown fuses are the result of either a power supply fault or a shorted output device. Start at the output transistors and work backwards.

 

Thanks PBG, I'll do that.

Oh and don't worry. The fuses are staying out and the power is staying off!!